Before the widespread use of microwave ovens, a typical container for popcorn making comprised a metal pan with a handle for supporting the corn kernels and suitable oils therein with an expandable thin metal sheet covering the pan. This pan was placed over a burner, thereby heating the corn kernels and oil, popping the kernels and forming the expanded popcorn. The expanded popcorn also expanded the thin metal sheet.
With the widespread use of microwave ovens, this type of packaging is inadequate since the metal pan and sheet insulate microwave energy and cannot thereby be used inside a microwave oven. In order to provide a package for use in a microwave oven, there has been proposed a paperboard expandable package as disclosed in U.S. Pat. No. 4,036,423, issued to R. L. Gordon. However, the package of the Gordon patent requires the application of adhesive to form the container for the kernels, which is time consuming and expensive to manufacture. In addition, it requires adhesive to lock the package in the closed position, which is also time consuming and expensive to manufacture. Moreover, this prior art package involves the folding of a plurality of flaps, on top of one another, which are then difficult to open during expansion of the popcorn therein.